The aims of our research in the coming year are to: 1) define the relationship of Ca2 ion to cGMP in the activation of the normal human peripheral lymphocyte; 2) continue studies on the metabolism and mode of action of vitamin D and its metabolites; 3) apply this knowledge to the improved diagnosis and treatment of metabolic bone diseases, particularly the use of 1 alpha (OH)D3 in the treatment of hypophosphatemic rickets; 4) define the biochemical modes of action of aldosterone and vasopressin upon Na ion and H2O transport in the toad urinary bladder, specifically the relationship between aldosterone- induced changes in phospholipid metabolism and its effects upon transcellular Na ion transport and the relationship between intracellular metabolism, intracellular Ca 2 ion and vasopressin action on bulk H20 flow in this tissue; and 5) study the role of intracellular Ca 2 ion in the regulation of red cell size, deformability, resistance to hypotonic hemmolysis, hemoglobin O2 saturation curves, and energy metabolism by using vasoactive hormones and calcium ionophores.